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Stock-Based Compensation - Stock Incentive Plan Activity, Restricted Stock (Details) - Restricted Stock Units (RSUs)
12 Months Ended
Dec. 31, 2018
$ / shares
shares
RSUs  
Balance (in shares) | shares 344,804
Granted (in shares) | shares 182,893
Vested (in shares) | shares (83,856)
Forfeited (in shares) | shares (33,976)
Balance (in shares) | shares 409,865
Weighted average grant date fair value  
Balance, weighted average grant date fair value (in dollars per share) | $ / shares $ 91.81
Granted, weighted average grant date fair value (in dollars per share) | $ / shares 86.84
Vested, weighted average grant date fair value (in dollars per share) | $ / shares 91.97
Forfeited, weighted average grant date fair value (in dollars per share) | $ / shares 94.33
Balance, weighted average grant date fair value (in dollars per share) | $ / shares $ 99.72